Interfacial stent and method of maintaining patency of surgical fenestrations

ABSTRACT

A method according to one embodiment for maintaining patency of an opening inside the human body comprises introducing a radially self-expanding hollow stent into the opening through an endoscope that radially compresses the stent, wherein the stent has enlarged ends and a reduced intermediate portion. The stent is introduced into the opening such that its intermediate portion extends through the opening and the enlarged ends are positioned outside of the opening. Once deployed, the stent expands such that the enlarged ends of the stent abut against opposing faces of the opening to resist dislodgement of the stent from the opening after expansion. The stent is preferably biodegradable, such that it is eliminated from the surgical site over a period of weeks to months, by which time the patency of the opening is more assured. The method can be used in combination with, for example, an endoscopic surgical method such as endoscopic third ventriculostomy for treating hydrocephalus of a brain.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit of U.S. ProvisionalApplication No. 60/570,178, filed May 11, 2004, which is incorporatedherein by reference.

STATEMENT OF GOVERNMENT SUPPORT

This invention has not been developed with any government support.

BACKGROUND OF THE INVENTION

The present disclosure relates to implantable stents used inside thehuman body for medical purposes.

The human body includes many anatomical pathways through which bodyfluids, such as blood or cerebrospinal fluid (CSF), must pass tomaintain proper biological function. Examples of such pathways areelongated blood vessels (such as the coronary arteries) and otherextended passageways that define a lumen (such as the aqueduct ofSylvius in the ventricular system of the brain). Obstructions ofbiological lumens can cause serious medical problems, such as tissueischemia secondary to occlusion of an artery, or hydrocephalus caused bydisruption of the flow of CSF through the ventricular system.

In the case of obstruction of an elongated vessel, such as stenosis of ablood vessel in the cardiovascular system, implantable intra-luminalstents have been used to maintain patency of the vessel lumen.Intravascular stents are commonly placed in an atherosclerotic coronaryartery to reestablish perfusion to ischemic cardiac tissue. Coronarystents are introduced along a catheter to a site of occlusion during anangioplasty procedure. The stents, which are typically tubular in shape,may be expanded mechanically or by the introduction of pressurized airinto a balloon placed in the lumen of the stent. Coronary stents are notusually designed to be biodegradable, because they are intended toprovide long-term mechanical support to maintain patency of the vessellumen.

In addition to using stents, surgeons often employ other operativetechniques to reestablish normal flow of fluids through biologicalpathways in the body. For example, an artificial opening such as asurgical fenestration may be created in a biological interface (such asa membrane or other tissue barrier) to either reopen a natural pathwayor to create a new pathway for therapeutic purposes. Endoscopic surgeryprocedures may involve fenestration of a biological interface inside thebody, in which a small opening is surgically created to establish orfacilitate communication of such fluids as blood, bile, aqueous humor orcerebrospinal fluid (CSF).

Endoscopic third ventriculostomy or endoscopic thirdventriculocistemostomy (ETV) is an example of a particular endoscopicprocedure performed to treat pathological disruption of normalbiological fluid flow. ETV is a procedure used for relievinghydrocephalus, a medical condition in which cerebrospinal fluid (CSF)accumulates in the ventricles of the brain due to obstruction of theflow of CSF within or from the ventricles. The accumulation of CSFincreases pressure inside the brain, which in turn causes enlargement ofthe cranium and compression of intracranial brain tissue. Hydrocephalusmost frequently occurs in young children, but is also found amongadults, and is usually accompanied by neurological deterioration ordeath.

A standard method to relieve hydrocephalus is to shunt CSF from thebrain into the abdominal, venous or peritoneal space. The shuntprocedure employs a valved CSF shunt system connected to a plasticdrainage line that diverts CSF out of the brain. A specific example ofthis procedure is ventriculoperitoneal (VP) drainage, which is commonlyused to treat hydrocephalus. However, such shunts often fail when theybecome infected or require surgical revision to relieve obstruction ofthe shunt. To help avoid such problems, endoscopic third ventriculostomy(ETV) is now commonly used to treat obstructive hydrocephalus, such asthat caused by an obstruction of the Aqueduct of Sylvius thatcommunicates between the third and fourth ventricles. ETV creates asurgical fenestration between the third ventricle and the subarachnoidspace to permit drainage of excess CSF.

ETV can be performed by placing a burr-hole anterior to the coronalsuture of the skull and introducing an endoscope through the brain, intothe lateral ventricle and through the foramen of Monro to gain access tothe floor of the third ventricle. A fenestration (a ventriculostomyopening) is then surgically created in the floor of the third ventricle,anterior to the basilar artery. The fenestration can be made, forexample, by introducing through the floor of the ventricle a blunt guidewire, closed forceps, laser, ultrasonic probe, or the tip of theendoscope itself. The fenestration hole is then enlarged toapproximately 5 mm by expanding the tip of a Fogarty balloon catheter inthe fenestration or by using an instrument designed for purposefuldilation of the fenestration. One advantage of the ETV procedure is thatit does not require an indwelling, permanent shunt catheter that issubject to occlusion or infection.

Although ETV has greatly improved the treatment of hydrocephalus, theventriculostomy opening sometimes becomes partially or completelyoccluded as scar tissue forms at the fenestration site. Even incarefully selected patients with obstructive hydrocephalus, technicallysuccessful endoscopic third ventriculostomy results in alleviation ofhydrocephalus in 60% to 70% of subjects, with up to 40% of subjectshaving an unsatisfactory clinical outcome. A significant proportion ofpatients who fail to respond to ETV suffer from secondary closure of theETV site due to scarring and/or arachnoidal adhesions, and may requiresubsequent surgical procedures to reestablish patency of the opening oralternatively may result in lifetime ventricular shunt dependency.

This problem with ETV illustrates a more general problem with manyendoscopic and other surgical procedures that create artificial openingsinside the human body. Surgically created openings in biologicalinterfaces, such as the walls of an organ or other anatomic structures,frequently close as a result of a normal inflammation and healingprocesses. It would therefore be useful to have a method or device thatwould maintain the patency of such openings for a sustained period oftime.

BRIEF SUMMARY OF THE DISCLOSURE

The present disclosure provides a method for maintaining patency of anopening through an interface inside the human body by introducing aradially self-expanding hollow stent into the opening through anendoscope that radially compresses the stent. The stent has enlargedends and a constricted intermediate portion. The shape of the stentallows it to be placed with its constricted intermediate portionsituated in the opening while the enlarged ends remain outside of theopening on opposite sides of the opening. The self-expanding stent isallowed to expand in situ such that the enlarged ends inhibitdislodgement of the stent from the opening. A lumen through the stentpermits the free flow of fluid through the opening while maintainingpatency of the opening.

In particular embodiments, the stent is biodegradable, such that itdegrades or otherwise dissolves over time (for example in one to sixmonths). Once the stent has degraded after this period of time, theincidence of scarring or other closure of the opening is reduced. Themethod can be implemented using an endoscopic surgical procedure fortreating hydrocephalus of the brain that increases the success rate ofthe surgery and reduces the chance of secondary failure. Such a methodcan include introducing an endoscope into the third ventricle of thebrain; fenestrating the floor of the third ventricle to create anopening that fluidly communicates between the third ventricle andsubarachnoid space; enlarging the opening; and placing the stent intothe opening.

Also disclosed herein is an interfacial stent for maintaining patency ofan opening in a biological interface (such as a wall of an organ orsubstructure thereof, such as a ventricle of a brain) in a human body.The stent includes two enlarged ends and a constricted intermediateportion. The stent is self-expandable, for example being made of amaterial that has resilient memory, and may be biodegradable. Inparticular examples, when the two enlarged ends are expanded, each has adiameter substantially greater than a diameter of the constrictedintermediate portion that extends through and fills the opening, and/orabout the same or greater than the length of the stent. In otherexamples, the stent has a substantially hollow body defined by an opensurface structure that allows flow of the body fluid therethrough.

In one example, the stent is made of bioabsorbable material thatdegrades in the body over a controlled period of time (such as one tosix months). The self-expandable nature of the stent allows it to beintroduced into an opening using a compression device (such as acatheter or endoscope lumen) that maintains the stent in a reduceddiameter state until it emerges from the device. After emergence, thestent radially expands to permit its secure deployment in the interfaceopening.

Other features and advantages of the invention will become more readilyunderstandable from the following detailed description and figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The present description of the stent and its method of use will bedescribed in detail along with the following figures, in which likeparts are denoted with like reference numerals or letters.

FIG. 1 is a schematic sagittal section view of the human brain in achild.

FIG. 2 is a schematic top view of a portion of the floor of the thirdventricle in the human brain, illustrating a surgical fenestration inthe floor of the ventricle.

FIG. 3 is a cross-sectional view of the floor of the third ventricleshowing a ventriculostomy hole.

FIG. 4 is a schematic view illustrating placement of the stent through afenestration in the floor of the ventricle using an endoscope.

FIG. 5 is another schematic view showing deployment of the stent throughthe fenestration.

FIG. 6 is another schematic view showing radial self-expansion of thestent within the fenestration.

FIG. 7 shows one example of a self-expandable stent in a compressed formas it would be found inside the endoscope prior to deployment.

FIG. 8 shows the stent of FIG. 7 after it has radially expanded.

FIG. 9 shows a second example of a self-expandable stent in a compressedform as it would be found inside the endoscope prior to deployment.

FIG. 10 shows the second exemplary self-expandable stent after it hasradially expanded.

DETAILED DESCRIPTION

A. Terms

In the present description, the terms “opening”, “hole”, “orifice”,“fenestration”, “perforation” and “stoma” all refer to an opening,either naturally existing or artificially created, through an interfaceof a human body part such as a tissue or membrane. Such interfaces maybe found either externally (for example through an ear lobe or otherskin surface) or internally (such as the wall of a hollow organ, or wallof a substructure of an organ, such as the ventricles of the brain orthe interventricular lumen). In contrast, the term “lumen” refers to theopen space within an elongated tubular vessel. Hence an opening, hole,fenestration or perforation is typically present in tissue interface, incontrast to a lumen, which extends through a tubular or elongatedextended tissue structure. In addition, the embodiments of the stentdisclosed herein are devised to maintain the patency of an artificiallycreated opening, instead of restoring patency of a pre-existing lumenthat has become occluded by a pathological process (such asatherosclerosis).

B. Disclosed Embodiments

The disclosed embodiments of the stent are generally designed tomaintain patency of an anatomic interface opening (such as a surgicallycreated fenestration) along the entire length of the opening, byretention of the stent within the interface opening by its enlarged endsdisposed on opposing faces of the opening. This is distinguished fromthe prior art use of a stent in a lumen of an elongated tubular vesselsuch as vascular artery, in which the stent occupies only anintermediate section of an elongated vessel and is contained entirelywithin the lumen of the elongated vessel.

Several representative embodiments of the stent and methods of its useare disclosed herein for purposes of illustrating how to make and usecertain examples of the invention. The representative embodiments arenot intended to be limiting in any way.

FIG. 1 shows a schematic sagittal section view of human brain 10.Viewable from the sagittal section view is a third ventricle 12, afourth ventricle 14, and an Aqueduct of Sylvius 16 which in a normalcondition communicates between third ventricle 12 and fourth ventricle14. CSF from fourth ventricle 14 circulates around spinal cord 18 whichdepends from the brainstem. Also shown in this view is the floor of thethird ventricle 20.

A subject who suffers obstructive hydrocephalus often has a blockage ofthe normal flow of CSF through the ventricular system and thesubarachnoid space. For example, a barrier to flow can form within anobstructed Aqueduct of Sylvius 16, which allows abnormal amounts of CSFto accumulate in the proximal portions of the ventricular system, forexample in the third ventricle 12 and lateral ventricles. This CSFaccumulation is a common cause of hydrocephalus which ultimately causesmegalocephaly (enlargement of the head), and compression of neuralpathways that leads to deterioration of neurological status, disabilityand/or death.

FIG. 2 is a schematic top view of wall 30 of the floor of the thirdventricle 20 in human brain 10. This view schematically represents whatis visible through an endoscope (not shown in FIG. 2) that is introducedinto the third ventricle 12 through an endoscopic channel thatcommunicates with a surgical opening through the skull anterior to thecoronal suture (not shown). Schematically shown in FIG. 2 are severalparts in the brain visible through the semi-transparent floor of thethird ventricle 20, including hypophyseal portal veins 35, pituitarygland 34, posterior cerebral artery 36, and posterior perforatingarteries 37.

During endoscopic third ventriculostomy (ETV), a fenestration 32 iscreated in the floor of third ventricle 20 to re-establish flow ofcerebrospinal fluid from the third ventricle 12 (FIG. 1) to thesubarachnoid space (not shown) underneath the floor of the thirdventricle 20. Various methods are known for making this fenestration,including mechanical means, laser and ultrasonic vibration. Usually,fenestration 32 needs to be enlarged after initial formation to achievea satisfactory size for the purpose of establishing a desired flow ofCSF. Enlargement may be performed using a catheter or using aninstrument designed for purposeful dilation of fenestrations. Thecatheter or the dilation instrument may be introduced through a workingchannel of the endoscope.

FIG. 3 shows a cross-sectional view of a portion of the floor of thirdventricle 30 in which fenestration 32 has been established. Fenestration32 is defined by perimeter edges 42 and 44. Where fenestration 32 has acircular shape, perimeter edges 42 and 44 are parts of the samecontinuous inner peripheral edge.

As previously discussed, up to 40% of ETV surgeries do not result insatisfactory resolution of hydrocephalus. A significant proportion ofpatients who fail to respond to ETV suffer from secondary re-closure oftheir ETV opening (fenestration 32) due to scarring and/or arachnoidaladhesion. This secondary occlusion of the fenestration can be avoided byuse of the embodiments of the stent disclosed herein. The stent istypically an elongated device having resilient memory that allows it toexpand from a radially compressed condition in which it is inserted intoopening 32 to a radially expanded condition in which it is securelyretained within opening 32.

FIGS. 4 and 5 show a stent 60, according to one embodiment, and onespecific approach for deploying the stent 60. The illustrated embodimentof stent 60 has a reduced diameter intermediate portion 57 (alsoreferred to herein as a constricted portion) and two relatively enlargedends 56, 58 that have a greater diameter than the diameter ofintermediate portion 57.

As shown in FIG. 4, after fenestration 32 has been created and enlarged,the tip of an endoscope is advanced toward fenestration 32 to deliverstent 60 from a delivery port 50 into fenestration 32. Endoscopicdelivery port 50 has an end 53 and sidewall 52 (both shown in phantom inFIG. 4). End 53 of port 50 is open for delivery of stent 60. Sidewall 52of port 50 confines stent 60 within port 50 and compresses it radiallyto reduce its diameter. This radial compression force temporarilymaintains stent 60 in a narrowed, reduced diameter condition (that mayor may not be also elongated compared to the deployed shape of thestent). A retractable release 59 disposed in the delivery port engagesthe proximal end 58 of stent 60.

As shown, release device 59 is advanced toward fenestration 32 throughthe delivery port 59 to deploy stent 60 out of delivery port 50 andplace it within fenestration 32, with intermediate portion 57 disposedwithin fenestration 32 and distal and proximal ends 56, 58 positionedoutside fenestration 32 on opposite faces of the wall 30 of thirdventricle 20. Once stent 60 has been deployed, and in the absence ofexternal compression, it radially expands as shown in FIG. 6 so that itsintermediate portion 57 abuts tightly against the borders of thefenestration, and ends 56, 58 expand to such an extent that stent 60resists longitudinal dislodgement in either direction out offenestration 32. For example, radially expanded ends 56 and 58 have adiameter D that is larger than that of constricted intermediate portion57 and also larger than the diameter of fenestration 32. In theparticular embodiment shown, diameter D of enlarged ends 56 and 58 isalso at least the same or greater than length L of the expanded stent60. Length L is measured along the longitudinal axis that issubstantially perpendicular to end faces 56A and 58A of ends 56 and 58of stent 60.

Intermediate portion 57 of radially expanded stent 60 abuts perimeteredges 42 and 44 of fenestration 32 to provide an anatomic barrier toclosure of the opening due to inflammatory or other healing processes.However, since stent 60 is hollow and both enlarged ends 56 and 58 areopen to fluid flow, retention of stent 60 within fenestration 32maintains patency of the fenestration 32.

Stent 60 is also preferably made of a bio-compatible material thatdegrades or otherwise spontaneously dissolves over a controlled orpredetermined period of time that is sufficient to inhibit closure offenestration 32. In many cases, natural inflammatory and healingprocesses, which initially tend to cause re-closure of thefenestrations, have by this point matured to form a stable and permanentscar tissue around the orifice, thus maintaining rather than occludingthe opening. Once the stent has degraded after this period of time, theincidence of scarring or other closure of the opening is reduced.

In a particular example, that period of time is at least one month, forexample one to six months. The time required for degrading the stent maybe determined based on the observations of a typical interval duringwhich a target opening may be subjected to undesired occlusion. Forexample, in ETV surgical procedures, the typical failure time duringwhich the ventriculostomy opening may spontaneously close is severalweeks. Accordingly, a suitable bioabsorbable material can be selectedfor making an ETV stent that degrades over several weeks after placementin the brain. For example, a material is chosen that is degraded by thecontinued flow of CSF through the stent in use. Gradual disappearance ofthe stent eliminates the necessity of surgical removal of the stent andalso reduces the potential risk for infection or other failure thataccompanies long term indwelling implants within the body. Furthermore,the bioabsorption time of the interfacial stent may be adjusted based onthe selection of the material and/or the construction of the stent(e.g., selecting a mesh or generally solid construction for the stent.)

In particular embodiments of the stent, it would have the followingdimensions: TABLE 1 Stent dimensions in Stent dimensions in compressedstate expanded state Outer diameters of two 2-5 mm 4-9 mm ends (56 and58) Length (L) 3-7 mm 2-4 mm Outer diameter of 2-4 mm 3-7 mmintermediate portion (57)

In one particular embodiment of the stent, outer diameters of ends 56and 58 are about 3.2 mm when compressed and 6 mm when expanded; length Lis 5 mm when compressed and 3 mm when expanded; and outer diameter ofintermediate portion 57 (waist) 57 is 3.2 mm when compressed and 5 mmwhen expanded.

Preferably, stent 60 is introduced into fenestration 32 during the sameprocedure in which the ventriculostomy fenestration is formed, such thatstent 60 is introduced into fenestration 32 immediately after formationof that opening. After stent 60 has been deployed into ventriculostomyopening 32, the endoscopic tools used to introduce the stent into theopening are withdrawn from the body while leaving stent 60 infenestration 32.

As shown in the above representative example, the present disclosureprovides a method and device for inhibiting re-closure of openings inthe human body, such as openings through biological interfaces that aredesigned to establish flow pathways. Re-closure is often caused bynatural healing processes in the human body. Such healing processes areparticularly effective in infants and young children, who indeed suffera particularly high failure rate after anatomically successful ETVprocedures. Infants and young children represent the majority ofpatients suffering from newly diagnosed obstructive hydrocephalus andthus would benefit most from the method and the stent of the presentdisclosure when applied in endoscopic third ventriculostomy.

The application of the method and the stent according to the presentdisclosure is not limited to ETV procedures. Examples of procedures inwhich maintenance of patency could be achieved in the disclosed fashioninclude a variety of cosmetic and therapeutic procedures. Patency ofopenings for body piercings could be assured, prior to introduction of ametal piercing, by placement of a biodegradable stent (which in thisinstance would not require a fluid passageway through it). Moreover,there are a number of therapeutic applications, such as maintainingpatency of trabeculoplasty, trabeculotomy or sclerotomy openings in theeye for treatment of glaucoma; typanostomy openings in the eardrum fortreatment of otitis media; tracheo-esphageal perforation for voicereconstruction after total laryngectomy; tracheostomy openings forestablishing a patent airway bypass; openings created in endoscopicnasal and/or facial sinus surgery for maintaining mucous drainagepathways; openings for maintaining bronchopleural fistula for chronicdrainage of pleural empyema and other disorders; and openings for themaintenance generally of other intentional permanent or semi-permanentfistulae in biological interfaces.

Although stent delivery has been described in connection with anendoscopic procedure, many other methods are known in the art that maybe used to deliver the interfacial stent. In an endoscopic applicationas shown in the above representative example, existing endoscopicdelivery systems may be readily adapted for delivery of the stent. Forexample, ETV surgery typically utilizes an endoscopic delivery port todeliver a catheter into the newly formed fenestration to enlarge thefenestration. The same endoscopic delivery port may be adapted fordelivery of the interfacial stent. Although the stent can be conceivablydeployed using a separate delivery port, sharing the same delivery portwith the catheter simplifies the system.

In one embodiment, stent 60 is self-expandable, meaning that it expandsautonomously when a compression force is removed, without requiring theapplication of external expansion forces (such as inflation of a balloonwithin the stent). One example of a self-expandable stent is a stentmade of a polymer that has resilient memory, such that the stent expandsin a controlled or predetermined fashion to assume a pre-configuredshape, usually a shape that the stent had before it was subjected tocompressive forces. Additional information about such polymers isprovided in a later section of this specification.

Stent 60 also can be bioabsorbable, meaning that the stent will bedissolved or absorbed over time within the human body after asufficient, usually predetermined period of time to maintain patency ofthe opening. In the present description, the terms “bioabsorbable”,“bioresorbable” and “biodegradable” have the same meaning andundistinguished from one another despite the awareness that some groupsof individuals in the art may regard these terms to have differentmeanings.

FIGS. 7 and 8 show additional configurations of a self-expandinginterfacial stent 60 for placement across an interface of the humanbody. Stent 60 has opposing ends 56 and 58 which are made of an elasticmaterial forming a ring at each end. A plurality of longitudinalmembers, or filaments, 64 run substantially parallel to each otherbetween ends 56 and 58 to connect the two ends. Filaments 64 define aninner passageway through which cerebrospinal fluid (or other biologicalfluid) can flow. Filaments 64 are made of a material having shapememory, as discussed further below, and are formed to at least partiallyremember a bent or bowed shape. FIG. 7 shows stent 60 in its radiallycompressed condition in which filaments 64 are axially stretched andends 56, 58 are spaced at a maximum distance from one another. FIG. 8shows stent 60 after it has been allowed to expand radially andfilaments 64 return to their remembered bowed shape. This radialexpansion makes stent 60 shorter, flatter and wider when deployed infenestration 32.

FIGS. 9 and 10 show yet another embodiment of a self-expanding hollowstent 70 that assumes a tubular configuration in its compressed state,for example conforming to a tubular shape of an endoscope lumen throughwhich stent 70 is introduced into the body. Stent 70 has opposing ends76 and 78 which are made of an elastic material forming a ring at eachend. Two sets of longitudinal members, or filaments, 72 and 74 are usedto form an interstitial mesh shaped outer surface that defines theboundary of stent 70. The interstitial mesh shaped outer surface definesa passageway through which cerebrospinal fluid (or other biologicalfluid) can flow. The two sets of filaments 72 and 74 each runsubstantially parallel with respect to the filaments in the same set butare slanted in different directions to form an angle between the twosets. Filaments 72 and 74 are made of a material having shape memory, asdiscussed further below, and formed to at least partially remember abent shape.

FIG. 9 shows stent 70 in the radially compressed state in whichfilaments 72 and 74 are axially stretched or elongated. FIG. 10 showsstent 70 after compression forces are removed to allow stent 70 toexpand radially as filaments 72 and 74 are allowed to return to theirremembered or non-compressed bent shape. This radial expansion makesstent 70 shorter and flatter. Compared to the embodiment in FIGS. 7 and8, the embodiment according to FIGS. 9 and 10 has a more stablestructure. As particularly illustrated in FIGS. 9 and 10, stent 70 hastwo frustoconical sections, each of which tapers from a respective end76, 78 to a common intermediate portion 77. The frustoconical sectionscan be separately formed and subsequently joined to each other at theirtapered ends to form the stent. In alternative embodiments, the stentcan comprise two tapered frustopyramidal sections, which can be formedin a similar manner. Stent 70 is illustrated as symmetric in shape,having both a transverse and longitudinal axis of symmetry.

Although illustrated in these examples as filamentous, stent 60 may alsobe made of appropriate sheet- or fabric-like materials with appropriateresilience and memory. The sheet- or fabric-like material may either bein an interstitial mesh pattern (either macroscopically ormicroscopically), or in a solid shape. The boundary formed by the sheet-or fabric-like material may be either permeable or impermeable to bodyfluids, as long as stent 60 has an open-ended hollow body thatfacilitates sufficient body fluid communication through the opening thatis intended to be sustained by stent 60.

C. Stent Fabrication

As far as the manufacturing methods are concerned, several types ofstents, including metal stents and polymer stents, may be suitable asthe trans-interface stent of the present disclosure, with polymer stentsbeing generally more preferable than metal stents.

Polymer Stents

Polymer stents include (but are not limited to) silicone, gelatin film,collagen film or matrix, polysaccharide matrices, and elastomer stents.Compared to metal stents, polymer stents are relatively newer products.One advantage that polymer stents have over metal stents is that theycan be bioabsorbable/biodegradable. For this reason, polymer stents aremore preferred for the applications disclosed herein.

An ideal stent may have the following characteristics (which are notessential requirements of the invention): (1) inexpensive tomanufacture; (2) easy to deploy; (3) sufficiently rigid to resist radialforces; and (4) disappears after treatment without leaving behindharmful residue. Polymer devices that have this capability includeresilient collagen materials, resilient gelatin films and biodegradablepolymers such as polyesters, polyorthoesters, polyanhydrides,polyglycolic acid and poly(glycerol-sebacate) or PGS. For example,although less flexible, polyglycolic acid tubes provide resultsequivalent to silicone rubber but are absorbed in seven days and therebyobviate the need for any additional procedure to remove the stent. Forapplications in which it is desired that the stent have resilientmemory, these biodegradable materials can be combined with otherpolymers that provide elastic recoil to a predetermined shape. Asuitable biodegradable polymer available commercially is GELFILM®, anabsorbable gelatin film made by Pharmacia & Upjohn (now a division ofPfizer).

Other suitable biodegradable polymers are discussed in U.S. Pat. No.6,719,934, which patent is incorporated by reference to the extent thatit discloses the polymers. These biodegradable polymers includepolylactide bioabsorbable polymer filaments, helically wound andinterwoven in a braided configuration to form a tube. Polylactidebioabsorbable polymer includes poly(alpha-hydroxy acid) such aspoly-L-lactide (PLLA), poly-D-lactide (PDLA), polyglycolide (PGA),polydioxanone, polycaprolactone, polygluconate, polylacticacid-polyethylene oxide copolymers, modified cellulose, collagen,poly(hydroxybutyrate), polyanhydride, polyphosphoester, poly(aminoacids), or related copolymers materials, each of which have acharacteristic degradation rate in the body. For example, PGA andpolydioxanone are relatively fast-bioabsorbing materials (weeks tomonths) and PLA and polycaprolactone are a relatively slow-bioabsorbingmaterial (months to years).

In addition, tyrosine-derived polycarbonate materials developed byIntegra LifeSciences Holdings Corp. (Plainsboro, N.J.) may also besuitable for making the interfacial stents of the present disclosure.Another suitable example is bioresorbable, biocompatible and resilientbovine collagen materials developed by Integra LifeSciences HoldingsCorp. Such collagen materials have been successfully used for variousdental and surgical purposes, but a resilient form of such materials,either in filaments or sheets, may also be a good choice for fabricatingthe stents of the present disclosure.

A particular example of a biodegradable, self-expandable stent is theL-lactide-glycolic acid co-polymer with a molar ratio of 80:20 (SR-PLGA80/20). This stent is sold under the product designation SpiroFlow (fromBionx Implants, Ltd., Tampere, Finland) and is disclosed in Laaksovirtaet al., J Urol. 2003 August; 170(2 Pt 1):468-71. See also Chepurov etal., Urologiia. 2003 May-June; (3):44-50.

Other bioresorbable polymers under investigation by others may also besuitable. For example, a bioresorbable polymer stent incorporatingnatural polymers has been described by Bier and coworkers (Bier, J. D.,et al., Journal of Interventional Cardiology, 1992. 5(3): p. 187-193.),where type I collagen was formed into a solid tube structure withoutslotted sides. Bioresorbable microporous intravascular stents wereconstructed by Ye and colleagues (Ye, Y -W., et al., ASAIO Journal,1996. 42: p. M823-M827. Ye, Y.-W., et al., Annals of BiomedicalEngineering, 1998. 26: p. 398-408.). These stents were extremely porous,and a gradient could be produced from various surfaces of the stent.

As noted, a stent constructed of a bioabsorbable polymer providescertain advantages relative to metal stents such as naturaldecomposition into non-toxic chemical species over a period, of time.Also, bioabsorbable polymeric stents may be manufactured at relativelylow manufacturing costs since vacuum heat treatment and chemicalcleaning commonly used in metal stent manufacturing are not required.

In addition, certain materials thought to be unsuitable for intraluminalstents used in vascular applications may be suitable for the stentsdisclosed herein. Intraluminal stents used in vascular applications havestringent requirements for materials to exhibit strong mechanicalproperties as structural support and desirable hemodynamics. Due to itsdistinctive application environment, interfacial stents may not requiresuch stringent mechanical properties for the materials. For example,unlike the endovascular environment, an interfacial environment is lesslikely to exert high mechanical stress on the stent.

Although multiple examples of embodiments have been disclosed, workersskilled in the art will recognize that changes may be made in form anddetail without departing from the spirit and scope of the invention.

1. A method for maintaining patency of an opening inside the human body,comprising: introducing a radially self-expanding hollow stent into theopening through an endoscope that radially compresses the stent, whereinthe stent has enlarged ends and an intermediate portion having a reducedcross-sectional profile, and the stent is introduced into the openingwith its intermediate portion extending through the opening and theenlarged ends positioned outside of the opening; and allowing theself-expanding stent to expand for retention within the opening by theenlarged ends on opposing faces of the opening.
 2. The method of claim1, wherein the stent is bioabsorbable, and degrades over time within thebody after a sufficient period of time to maintain patency of theopening.
 3. The method of claim 1, further comprising forming theopening by forming a surgical fenestration inside the human body.
 4. Themethod of claim 3, wherein the surgical fenestration is formed in a wallof a ventricle of the brain to establish a path of cerebrospinal fluidflow from the ventricle to a sub-arachnoid space.
 5. The method of claim4, wherein the surgical fenestration is formed in a floor of the thirdventricle.
 6. The method of claim 3, wherein introducing the radiallyself-expanding hollow stent into the opening takes place substantiallyimmediately after the fenestration has been artificially created.
 7. Themethod of claim 1, wherein the stent comprises a resilient material thatis compressed by delivery through the endoscope, but which expands afterdelivery from the endoscope into the opening.
 8. The method of claim 7,wherein the resilient material comprises L-lactide-glycolic acidco-polymer with a molar ratio of 80:20 (SR-PLGA 80/20), a biocompatiblepolymer, a biocompatible elastomer, a resilient collagen material, apolysaccharide matrix, or a bioabsorbable gelatin film.
 9. The method ofclaim 1, wherein the intermediate portion is a tapered intermediateportion.
 10. The method of claim 9, wherein the stent is symmetric inshape.
 11. The method of claim 10, wherein the stent comprises twojoined frustoconical sections.
 12. The method of claim 1, wherein thestent further comprises a material having shape memory such that thestent is stretchable into an elongated shape along a longitudinaldirection and at least partially returns to a remembered shape throughexpanding along a radial direction.
 13. The method of claim 12, whereinthe stent comprises multiple longitudinally extending filaments made ofthe material having shape memory.
 14. The method of claim 13, whereinthe multiple filaments comprise an interstitial mesh.
 15. The stent ofclaim 1, wherein the enlarged ends of the stent each comprise an elasticmaterial.
 16. The method of claim 1, further comprising withdrawing fromthe opening any surgical instrument used for introducing the stent intothe opening to leave the stent in the opening.
 17. The method of claim1, wherein introducing the stent into the opening comprises introducingthe stent using an endoscopic surgical procedure.
 18. The method ofclaim 17, wherein using an endoscopic surgical procedure comprisesproviding a multifunctional telescopic port that is used forsequentially creating the opening and delivering the stent.
 19. Themethod of claim 1, wherein the stent is introduced into the openingthrough an endoscopic delivery port, the stent being constrained withina tubular portion of the delivery port and held by a retractable releasedevice before being introduced into the opening.
 20. The method of claim1, wherein the intermediate portion contacts an edge of the openingafter the stent has expanded.
 21. An endoscopic surgical method fortreating hydrocephalus of a brain, comprising: introducing an endoscopeinto the third ventricle of the brain; fenestrating the floor of thethird ventricle to create an opening fluidly communicating between thethird ventricle and a subarachnoid space; enlarging the opening; placinga stent into the opening; and retrieving from the opening any surgicalinstrument used for placing the stent into the opening to leave thestent in the opening to maintain the patency of the opening.
 22. Themethod of claim 21, wherein the stent comprises a distal portion with adistal end, an intermediate portion, and a proximal portion with aproximal end, and after the stent has been introduced into the opening,the proximal end and the distal end each have a diameter greater thanthe opening, and the proximal end and the distal end are on two opposingsides of the opening while the intermediate portion passes through theopening.
 23. The method of claim 22, wherein the intermediate portion ofthe stent has a diameter smaller than the diameters of the distal endand the proximal end.
 24. The method of claim 23, wherein the stenttapers from the proximal end and the distal end toward the intermediateportion.
 25. The method of claim 21, wherein the distal portion and theproximal portion each have a frustoconical or frustopyramidal shape. 26.The method of claim 21, wherein the stent is bioabsorbable.
 27. Themethod of claim 21, wherein the stent is self-expandable.
 28. The methodof claim 21, wherein placing the stent into the opening furthercomprises: delivering the stent through an endoscopic delivery portadjacent the opening, wherein the stent is advanced through theendoscopic delivery port by a retractable delivery device; releasing thestent; allowing the stent to expand such that the proximal end and thedistal end each expand from a first diameter to a second diameter,wherein the second diameter of the proximal end and the second diameterof the distal end are both greater than the opening.
 29. The method ofclaim 28, wherein the stent is delivered into the opening before it isreleased by the retractable delivery device.
 30. A stent for maintainingpatency of an opening at an interface in a human body, the stentcomprising: two enlarged ends; and an intermediate portion defining across-sectional profile that is smaller than that of the enlarged ends;wherein the stent is biodegradable and expandable; wherein the stentcomprises a substantially hollow body defined by an open surfacestructure which allows flow of a body fluid through the stent.
 31. Thestent of claim 30, wherein the stent is self-expandable.
 32. The stentof claim 30, wherein the stent is bioabsorbable.
 33. The stent of claim30, wherein the stent tapers from the enlarged ends toward a locationintermediate the enlarged ends.
 34. The stent of claim 33, wherein thestent is symmetric in shape with respect to an axial direction.
 35. Thestent of claim 34, wherein the stent comprises two joined frustoconicalsections.
 36. The stent of claim 30, wherein the open surface structureis an interstitial mesh of filaments.
 37. The stent of claim 30, whereinthe stent comprises a resilient material.
 38. The stent of claim 37,wherein the resilient material comprises L-lactide-glycolic acidco-polymer with a molar ratio of 80:20 (SR-PLGA 80/20), a biocompatiblepolymer, a biocompatible elastomer, a resilient collagen material, apolysaccharide matrix, or a bioabsorbable gelatin film.
 39. The stent ofclaim 30, wherein the stent comprises a material having shape memory.40. The stent of claim 30, wherein the enlarged ends comprise an elasticmaterial.
 41. The stent of claim 30, wherein the stent comprisesmultiple filaments extending between the enlarged ends, the filamentsbeing made of a resilient material.
 42. The stent of claim 30, whereinwhen expanded the two enlarged ends have a diameter about the same orgreater than a length of the stent.
 43. An artificial fluid pathwaycreated in a membrane in a biological body such as a human body tofacilitate fluidic communication, comprising: an artificially createdopening in the membrane; and a hollow stent situated in the opening,wherein the stent has enlarged ends and a constricted intermediateportion, the intermediate portion extending through the opening and theenlarged ends being positioned outside of the opening, and wherein thestent is capable of maintaining the patency of the opening for anextended period of time without support of an additional surgicalmember.